Using the Microsoft Defender for Endpoint Files API to Validate Malware Hashes
Introduction Security advisories frequently include file hashes (SHA-1 or SHA-256) as indicators of compromise (IoCs). Microsoft Defender for Endpoint (MDE) exposes a Files API that lets SecOps quickly look up Microsoft’s verdict and metadata for a given hash. This enables rapid assessment—whether a file is classified as Malicious, Suspicious, Clean, or Unknown—and helps analysts decide the next response action without needing to download or execute the sample. What is the Files API in MDE and why is it used in Security Operations? The Files API is part of the Defender for Endpoint REST APIs that returns a file profile by hash identifier. Analysts use it to: • Validate whether Microsoft has a global verdict for a hash named in an advisory. • Retrieve telemetry such as global prevalence and first/last observed times to gauge risk and spread. • Pivot to related alerts and devices when needed. This lookup shortens triage time and avoids unnecessary handling of potentially dangerous samples. Prerequisites To call the Files API using application (client credentials) context, you need: A Microsoft Entra ID App Registration (Web app / service). API permissions on the WindowsDefenderATP resource (Microsoft Defender for Endpoint). Minimum: File.Read.All (Application). Admin consent granted for the permissions. Network access to the MDE API endpoint (region-based base URL) and the Microsoft identity platform (OAuth 2.0). Tip: For interactive testing, you can also use the API Explorer in the Microsoft Defender portal under Partners & APIs, which runs requests under your user context and RBAC scope. How to use the Files API via PowerShell 1) Acquire an OAuth token from the Microsoft identity platform using your app’s client ID and secret with the .default scope for the Defender API. 2) Send an HTTP GET request to the Files endpoint with the hash (SHA-1 or SHA-256) as the identifier. 3) Inspect the JSON response field "fileClassification" and other metadata (globalPrevalence, first/last observed). 4) Use the verdict to decide next actions (e.g., create an Indicator to block, hunt in Advanced Hunting, or open related alerts). Actual Script ===== STEP 1: Get OAuth Token (MDE v1) ===== $tenantId = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" $appId = "xxxxxxxxxxxxxxxxxxxxxxxxxxx" $appSecret = "xxxxxxxxxxxxxxxxxxxxxxxxxxx" # update with your tenant and app values $tokenUri = "https://login.microsoftonline.com/$tenantId/oauth2/v2.0/token" $body = @{ client_id = $appId scope = "https://api.securitycenter.microsoft.com/.default" client_secret = $appSecret grant_type = "client_credentials" } $tokenResponse = Invoke-RestMethod -Uri $tokenUri -Method Post -Body $body -ContentType "application/x-www-form-urlencoded" $token = $tokenResponse.access_token # ===== STEP 2: Call MDE v1 Files API ===== $hash = "97bf5e1a903a978b2281496e0a897688e9d8e6f981238cf91e39bae20390defe" # Replace with your actual hash values. $uri = "https://api.securitycenter.microsoft.com/api/v1.0/files/$hash" try { $response = Invoke-RestMethod -Uri $uri -Headers @{ Authorization = "Bearer $token" Accept = "application/json" } -Method Get } catch { Write-Error "API call failed: $($_.Exception.Message)" if ($_.ErrorDetails.Message) { Write-Host $_.ErrorDetails.Message } return } switch ($response.fileClassification) { "Malicious" { Write-Host "MDE recognises this hash as MALICIOUS. Threat Name: $($response.threatName)" -ForegroundColor Red } "Suspicious" { Write-Host "MDE recognises this hash as SUSPICIOUS." -ForegroundColor Yellow } "Clean" { Write-Host "MDE recognises this hash as CLEAN." -ForegroundColor Green } default { Write-Host "MDE does NOT have a signature for this hash (Unknown)." -ForegroundColor Gray } } $response | ConvertTo-Json -Depth 5 Script Explanation Token acquisition: Uses OAuth 2.0 client credentials flow to obtain an access token; scope targets Defender for Endpoint API. Endpoint call: Builds a GET request to the Files endpoint with the hash identifier. Error handling: Catches HTTP errors and prints server-provided details if available. Verdict mapping: Reads the fileClassification field and prints a color-coded verdict (Malicious, Suspicious, Clean, Unknown). Response output: Prints the full JSON for deeper analysis and logging. Recommended Inputs The Files endpoint accepts SHA-1 or SHA-256 identifiers; ensure you pass the correct hash type. Consider using certificate credentials or managed identity instead of client secrets for production automation. Sample Output API Explorer - Other Option to query File API The Microsoft Defender for Endpoint API Explorer is a tool that helps you explore various Defender for Endpoint APIs interactively. The API Explorer makes it easy to construct and do API queries, test, and send requests for any available Defender for Endpoint API endpoint. Use the API Explorer to take actions or find data that might not yet be available through the user interface. The tool is useful during app development. It allows you to perform API queries that respect your user access settings, reducing the need to generate access tokens. You can also use the tool to explore the gallery of sample queries, copy result code samples, and generate debug information. With the API Explorer, you can: Run requests for any method and see responses in real-time. Quickly browse through the API samples and learn what parameters they support. Make API calls with ease; no need to authenticate beyond the management portal signin. Access API Explorer From the left navigation menu, select Partners & APIs > API Explorer. Supported APIs API Explorer supports all the APIs offered by Defender for Endpoint. The list of supported APIs is available in the APIs documentation. Get started with the API Explorer In the left pane, there's a list of sample requests that you can use. Follow the links and click Run query. Some of the samples may require specifying a parameter in the URL, for example, {File Hash}. Permissions Required You need to log in with an account that has appropriate RBAC roles in Microsoft Defender for Endpoint. API Explorer enforces the same role-based access control (RBAC) as the portal: Security Administrator or Global Administrator for high-privilege actions (e.g., offboarding a device, submitting indicators). Lower roles (e.g., Security Reader) can only run read-only queries like Get file information or Get alerts. No additional API permissions or app registration are needed because requests run under your user context. Conclusion The MDE Files API gives SecOps an immediate way to validate hashes from advisories and threat feeds, reducing time-to-triage and enabling consistent response. When a hash is classified as Malicious or Suspicious, teams can move directly to containment (e.g., creating an Indicator to block). When it is Clean or Unknown, analysts can pivot to hunting, sandboxing, or further intelligence before acting. Integrating this lookup into runbooks helps security operations quickly and safely respond to emerging threats. References Get file information API: https://learn.microsoft.com/en-us/defender-endpoint/api/get-file-information Supported MDE APIs (Endpoint URI & versioning): https://learn.microsoft.com/en-us/defender-endpoint/api/exposed-apis-list Access the Microsoft Defender for Endpoint APIs (intro & app context): https://learn.microsoft.com/en-us/defender-endpoint/api/apis-intro Create an app to access MDE without a user (app registration & permissions): https://learn.microsoft.com/en-us/defender-endpoint/api/exposed-apis-create-app-webapp API Explorer: https://learn.microsoft.com/en-us/defender-endpoint/api/api-explorer
Can I check whether an IoC/hash is already monitored by MDE?
The list of IoC is limited to 15k. I imagine some IoCs entries from our "custom list" are already monitored by Microsoft/MDE. So, is there a way to check whether there is a detection rule for a specific IoC (hash)? This would save us some thousand entries and improve our monitoring coverage. *Better to join forces than reinvent the wheel.
Permission required to import to Indicators page? Error "Failed to Import Indicators"
Hello, Do you need the permission "Manage security settings in Security Center" in order to import xslx to Indicators? User getting error "Failed to import indicators. User is not exposed to all Indicator's machine groups. Contact your administrator for further information." User is in role. Role is setup with a group that has all the permissions expect "Manage security settings in Security Center". Role also has access to device groups that are setup. https://docs.microsoft.com/en-us/microsoft-365/security/defender-endpoint/user-roles?view=o365-worldwide#permission-options -Link above doesn't list "Indicators" in permission options Can not find the answer based on Googling Thanks!Indicators enhancements: Allow/Block by certificates & more
We’re excited to share that you can now set an indicator to prevent and exclude entities based on certificate information. In addition, the alert and block action on files can now be applied on files signed by trusted publishers. We have also increased the number of custom indicators you can create from 5,000 to 15,000.
